The goals of this proposal are to develop viable syntheses of a broad range of polycyclopentanoid natural products. The principal target molecules include: (a) Capnellenediol, a marine natural product responsible for the atypical behavior of the soft coral Capnella imbricata to ward off algae and other microbial growth; (b) pentalenic acid, a triquinane structure produced by several strains of Streptomyces as a biosynthetic precursor to the lipophilic antibiotic pentalenolactone; (c) retigeranic acid, a structurally unique pentacyclic sesterterpene isolated from Lobaria retigera and containing eight chiral centers and five quaternary carbons in its carbocyclic network; (d) magellanine, a new type of lycopodium alkaloid which has been isolated in quantities too small to permit pharmacological evaluation; (e) trixikingolide, a chemotaxonomically important sesquiterpene, which possesses a highly condensed pentacyclic network of carbon atoms; and ikarugamycin, an antibiotic of novel structure which possesses specific antiprotozoal activity of a high order and is a member of a growing class of important tetramic acid-based antibiotics. In many of these examples, our goal is to prepare the target molecules in proper optically active form by schemes which will prove to be not only preparatively useful, but amenable also to modification so that analogues can be obtained if biological activity warrants expansion of the effort.